Light emitting device and projector

ABSTRACT

A light emitting device includes a laminated structure having a plurality of columnar parts, wherein the columnar part includes a first semiconductor layer, a second semiconductor layer different in conductivity type from the first semiconductor layer, and a third semiconductor layer disposed between the first semiconductor layer and the second semiconductor layer, the third semiconductor layer includes a light emitting layer, and the second semiconductor layer includes a first portion, and a second portion which surrounds the first portion in a plan view from a laminating direction of the first semiconductor layer and the light emitting layer, and is lower in impurity concentration than the first portion.

The present application is based on, and claims priority from JPApplication Serial Number 2020-129993, filed Jul. 31, 2020, thedisclosure of which is hereby incorporated by reference herein in itsentirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a light emitting device and aprojector.

2. Related Art

Semiconductor lasers are promised as high-luminance next-generationlight sources. In particular, the semiconductor laser having anano-structure called a nano-column, a nano-wire, a nano-rod, anano-pillar, or the like is expected to realize a light emitting devicecapable of obtaining light emission narrow in radiation angle and highin power due to an effect of a photonic crystal.

For example, in JP-A-2013-239718, there is described a semiconductorphotonic device array provided with a fine column crystal including ann-type cladding layer growing above a mask pattern, an active layer, anda p-type semiconductor layer.

In the semiconductor photonic element array provided with suchnano-columns as described above, a crystal fault is apt to occur in aside surface of the nano-column. The crystal fault forms a leakage pathof an electrical current between an n-type semiconductor layer and ap-type semiconductor layer in some cases.

SUMMARY

A light emitting device according to an aspect of the present disclosureincludes a laminated structure having a plurality of columnar parts,wherein the columnar part includes a first semiconductor layer, a secondsemiconductor layer different in conductivity type from the firstsemiconductor layer, and a third semiconductor layer disposed betweenthe first semiconductor layer and the second semiconductor layer, thethird semiconductor layer includes a light emitting layer, and thesecond semiconductor layer includes a first portion, and a secondportion which surrounds the first portion in a plan view from alaminating direction of the first semiconductor layer and the lightemitting layer, and is lower in impurity concentration than the firstportion.

A projector according to another aspect of the present disclosureincludes the light emitting device according to the above aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically showing the lightemitting device according to the embodiment.

FIG. 2 is a cross-sectional view schematically showing a columnar partof the light emitting device according to the embodiment.

FIG. 3 is a plan view schematically showing the columnar part of thelight emitting device according to the embodiment.

FIG. 4 is a cross-sectional view schematically showing a columnar partof a light emitting device according to a modified example of theembodiment.

FIG. 5 is a cross-sectional view schematically showing a manufacturingprocess of the light emitting device according to the embodiment.

FIG. 6 is a diagram schematically showing a projector according to theembodiment.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT

A preferred embodiment of the present disclosure will hereinafter bedescribed in detail using the drawings. It should be noted that theembodiments described hereinafter do not unreasonably limit the contentsof the present disclosure as set forth in the appended claims. Further,all of the constituents described hereinafter are not necessarilyessential elements of the present disclosure.

1. Light Emitting Device

First, a light emitting device according to the present embodiment willbe described with reference to the accompanying drawings. FIG. 1 is across-sectional view schematically showing the light emitting device 100according to the present embodiment. FIG. 2 is a cross-sectional viewschematically showing one of columnar parts 30 of the light emittingdevice 100 according to the present embodiment. It should be noted thatin FIG. 1, the columnar parts 30 are illustrated in a simplified mannerfor the sake of convenience.

As shown in FIG. 1, the light emitting device 100 has, for example, asubstrate 10, a laminated structure 20, a first electrode 110, and asecond electrode 112.

The substrate 10 is, for example, an Si substrate, a GaN substrate, or asapphire substrate.

The laminated structure 20 is provided to the substrate 10. Thelaminated structure 20 has a buffer layer 22, the columnar parts 30, anda light propagation layer 90.

The buffer layer 22 is disposed on the substrate 10. The buffer layer 22is, for example, an Si-doped n-type GaN layer.

In the present specification, when taking the light emitting layer 60 asa reference in a laminating direction of a first semiconductor layer 40and a light emitting layer 60 (hereinafter also referred to simply as a“laminating direction”), the description will be presented assuming adirection from the light emitting layer 60 toward a second semiconductorlayer 80 as an “upward direction,” and a direction from the lightemitting layer 60 toward the first semiconductor layer 40 as a “downwarddirection.” Further, a direction perpendicular to the laminatingdirection is also referred to as an “in-plane direction.”

The buffer layer 22 is disposed on the substrate 10. The buffer layer 22is, for example, an Si-doped n-type GaN layer. It should be noted thatalthough not shown in the drawings, it is possible to dispose a masklayer for growing the columnar parts 30 on the buffer layer. The masklayer is, for example, a silicon oxide layer, a titanium layer, atitanium oxide layer, or an aluminum oxide layer.

The columnar parts 30 are disposed on the buffer layer 22. The columnarparts 30 each have a columnar shape protruding upward from the bufferlayer 22. The columnar part 30 is also referred to as, for example, anano-column, a nano-wire, a nano-rod, or a nano-pillar. A planar shapeof the columnar part 30 is, for example, a polygon such as a regularhexagon, or a circle.

The diametrical size of the columnar part 30 is, for example, no smallerthan 50 nm and no larger than 500 nm. By setting the diametrical size ofthe columnar part 30 to be no larger than 500 nm, it is possible toobtain the light emitting layer 60 made of crystals high in quality, andat the same time, it is possible to reduce a distortion inherent in thelight emitting layer 60. Thus, it is possible to amplify light generatedin the light emitting layer 60 with high efficiency. The columnar parts30 are, for example, equal in diametrical size to each other.

It should be noted that when the planar shape of the columnar part 30 isa circle, the “diametrical size of the columnar part” means the diameterof the circle, and when the planar shape of the columnar part 30 is nota circular shape, the “diametrical size of the columnar part” means thediameter of the minimum bounding circle. For example, when the planarshape of the columnar part 30 is a polygonal shape, the diametrical sizeof the columnar part 30 is the diameter of a minimum circle includingthe polygonal shape inside, and when the planar shape of the columnarpart 30 is an ellipse, the diametrical size of the columnar part 30 isthe diameter of a minimum circle including the ellipse inside.

The number of the columnar parts 30 disposed is two or more. An intervalbetween the columnar parts 30 adjacent to each other is, for example, nosmaller than 1 nm and no larger than 500 nm. The columnar parts 30 arearranged at a predetermined pitch in a predetermined direction in a planview from the laminating direction (hereinafter also referred to simplyas “in the plan view”) . The plurality of columnar parts 30 is arrangedso as to form, for example, a triangular lattice. It should be notedthat the arrangement of the plurality of columnar parts 30 is notparticularly limited, and the plurality of columnar parts 30 can bearranged to form a square lattice. The plurality of columnar parts 30can develop an effect of a photonic crystal.

It should be noted that the “pitch of the columnar parts” means adistance between the centers of the columnar parts 30 adjacent to eachother along the predetermined direction. When the planar shape of thecolumnar part 30 is a circle, the “center of the columnar part” meansthe center of the circle, and when the planar shape of the columnar part30 is not a circular shape, the “center of the columnar part” means thecenter of the minimum bounding circle. For example, when the planarshape of the columnar part 30 is a polygonal shape, the center of thecolumnar part 30 is the center of a minimum circle including thepolygonal shape inside, and when the planar shape of the columnar part30 is an ellipse, the center of the columnar part 30 is the center of aminimum circle including the ellipse inside.

As shown in FIG. 2, the columnar part 30 has, for example, the firstsemiconductor layer 40, the second semiconductor layer 80, and a thirdsemiconductor layer 102.

The third semiconductor layer 102 is formed of a plurality ofsemiconductor layers. The third semiconductor layer 102 has a firstoptical confinement layer (OCL) 50, a hole blocking layer (HBL) 52, alight emitting layer 60, a second optical confinement layer 70, and anelectron blocking layer (EBL) 72.

The first semiconductor layer 40 is disposed on the buffer layer 22. Thefirst semiconductor layer 40 is disposed between the substrate 10 andthe light emitting layer 60. The first semiconductor layer 40 is ann-type semiconductor layer. The first semiconductor layer 40 is, forexample, an Si-doped n-type GaN layer. The first semiconductor layer 40has, for example, a high concentration part 42 and a low concentrationpart 44.

In the first semiconductor layer 40, an impurity concentration of thehigh concentration part 42 is higher than an impurity concentration ofthe low concentration part 44. A diametrical size D2 at the lightemitting layer 60 side of the high concentration part 42 is smallerthan, for example, a diametrical size D1 at an opposite side to thelight emitting layer 60 of the high concentration part 42. Thediametrical size D1 is a diametrical size in a portion the closest tothe substrate 10 in the high concentration part 42. The diametrical sizeD1 is, for example, a diametrical size in a contact portion of the highconcentration part 42 with the buffer layer 22. The diametrical size D2is a diametrical size in a portion the closest to the light emittinglayer 60 in the high concentration part 42. In the illustrated example,the diametrical size D2 is a diametrical size in a contact portion ofthe high concentration part 42 with the first optical confinement layer50. A shape of the high concentration part 42 is, for example, a tapershape the diametrical size of which gradually decreases in a directionfrom the substrate 10 toward the light emitting layer 60. It should benoted that although not shown in the drawings, the diametrical size D2can be the same as the diametrical size D1.

In the first semiconductor layer 40, the impurity concentration of thelow concentration part 44 is lower than the impurity concentration ofthe high concentration part 42. The low concentration part 44 surroundsthe high concentration part 42 in the plan view. The fact that theimpurity concentration of the low concentration part 44 is lower thanthe impurity concentration of the high concentration part 42 can beconfirmed by, for example, an atom probe analysis method.

The first optical confinement layer 50 is disposed on the firstsemiconductor layer 40. The first optical confinement layer 50 isdisposed between the first semiconductor layer 40 and the light emittinglayer 60. The first optical confinement layer 50 is, for example, anSi-doped n-type InGaN layer. When the first optical confinement layer 50and a well layer 62 are each an InGaN layer, an atomic concentration (at%) of In in the first optical confinement layer 50 is lower than anatomic concentration of In in the well layer 62. The first opticalconfinement layer 50 is not limited to the InGaN layer, and can also be,for example, an AlGaN layer or an InAlGaN layer. The first opticalconfinement layer 50 is capable of reducing the light to be leaked fromthe light emitting layer 60 toward the first semiconductor layer 40.

The hole blocking layer 52 is disposed on the first optical confinementlayer 50. The hole blocking layer 52 is disposed between the firstsemiconductor layer 40 and the light emitting layer 60. The holeblocking layer 52 has, for example, a c-plane 52 a and a facet plane 52b. In the illustrated example, the c-plane 52 a is an upper surface ofthe hole blocking layer 52. The facet plane 52 b is a side surface ofthe hole blocking layer 52.

The hole blocking layer 52 is, for example, an Si-doped n-type InGaNlayer. When the hole blocking layer 52 and the well layer 62 of thelight emitting layer 60 are each an InGaN layer, an atomic concentrationof In in the hole blocking layer 52 is lower than the atomicconcentration of In in the well layer 62. The hole blocking layer 52 iscapable of reducing the holes to be leaked from the light emitting layer60 toward the first semiconductor layer 40.

It should be noted that although in the illustrated example, the holeblocking layer 52 is disposed on the first optical confinement layer 50,this is not a limitation, and it is possible to dispose the holeblocking layer 52 on the first semiconductor layer 40, and dispose thefirst optical confinement layer 50 on the hole blocking layer 52.

The light emitting layer 60 is disposed on the hole blocking layer 52.The light emitting layer 60 is disposed on the c-plane of the holeblocking layer 52. The light emitting layer 60 is disposed between thefirst semiconductor layer 40 and the second semiconductor layer 80. Thelight emitting layer 60 generates light in response to injection of anelectrical current.

The light emitting layer 60 has the well layers 62 and barrier layers64. The well layers 62 are each, for example, an i-type InGaN layerdoped with no impurity. The number of the well layers 62 disposed is twoor more. The barrier layers 64 are each, for example, an i-type GaNlayer. The number of the barrier layers 64 disposed is two or more. Thelight emitting layer 60 has a multiple quantum well structure obtainedby stacking quantum well structures each constituted by the well layer62 and the barrier layer 64 on one another. In the illustrated example,the barrier layers 64 adjacent to each other are continuous in aperipheral part of the light emitting layer 60. The well layer 62 issurrounded by the barrier layer 64 in the plan view.

The light emitting layer 60 has a c-plane 60 a and a facet plane 60 b.In the illustrated example, the c-plane 60 a is an upper surface of thelight emitting layer 60. The facet plane 60 b is a side surface of thelight emitting layer 60. In the illustrated example, the c-plane 60 aand the facet plane 60 b are formed of the barrier layers 64.

A diametrical size D3 at the high concentration part 42 side of thelight emitting layer 60 is larger than the diametrical size D2 at thelight emitting layer 60 side of the high concentration part 42. Thediametrical size D3 is a diametrical size in a portion the closest tothe high concentration part 42 in the light emitting layer 60. In theillustrated example, the diametrical size D3 is a diametrical size in acontact portion of the light emitting layer 60 with the hole blockinglayer 52.

The second optical confinement layer 70 is disposed on the lightemitting layer 60. The second optical confinement layer 70 is disposedbetween the light emitting layer 60 and the second semiconductor layer80. The second optical confinement layer 70 is disposed on the c-plane60 a of the light emitting layer 60. The second optical confinementlayer 70 has a c-plane 70 a and a facet plane 70 b. In the illustratedexample, the c-plane 70 a is an upper surface of the second opticalconfinement layer 70. The facet plane 70 b is a side surface of thesecond optical confinement layer 70.

The second optical confinement layer 70 is, for example, an Mg-dopedp-type InGaN layer. When the second optical confinement layer 70 and thewell layers 62 are each an InGaN layer, an atomic concentration of In inthe second optical confinement layer 70 is lower than an atomicconcentration of In in the well layer 62. The second optical confinementlayer 70 is capable of reducing the light to be leaked from the lightemitting layer 60 toward the second semiconductor layer 80. In theillustrated example, the shapes of the second optical confinement layer70, the light emitting layer 60, and the hole blocking layer 52 are eacha taper shape the diametrical size of which gradually decreases in adirection from the first semiconductor layer 40 toward a highconcentration part 82 of the second semiconductor layer 80.

The electron blocking layer 72 is disposed on the second opticalconfinement layer 70. The electron blocking layer 72 is disposed betweenthe light emitting layer 60 and the second semiconductor layer 80. Inthe illustrated example, the electron blocking layer 72 is disposed onthe c-plane 70 a and the facet plane 70 b of the second opticalconfinement layer 70, the facet plane 60 b of the light emitting layer60, and the facet plane 52 b of the hole blocking layer 52. The electronblocking layer 72 has a c-plane 72 a and a facet plane 72 b. In theillustrated example, the c-plane 72 a is an upper surface of theelectron blocking layer 72. The facet plane 72 b is a side surface ofthe electron blocking layer 72. The c-planes 52 a, 60 a, 70 a, and 72 aare parallel to, for example, the upper surface of the substrate 10. Thefacet planes 52 b, 60 b, 70 b, and 72 b are tilted with respect to theupper surface of the substrate 10.

The electron blocking layer 72 is, for example, an Mg-doped p-type AlGaNlayer. The electron blocking layer 72 is capable of reducing theelectrons to be leaked from the light emitting layer 60 toward thesecond semiconductor layer 80.

The second semiconductor layer 80 is disposed on the electron blockinglayer 72. The second semiconductor layer 80 is disposed between thelight emitting layer 60 and the second electrode 112. The secondsemiconductor layer 80 is a semiconductor layer different inconductivity type from the first semiconductor layer 40. The secondsemiconductor layer 80 is a p-type semiconductor layer. The secondsemiconductor layer 80 is, for example, an Mg-doped p-type GaN layer.The first semiconductor layer 40 and the second semiconductor layer 80are cladding layers having a function of confining the light in thelight emitting layer 60. The second semiconductor layer 80 has the highconcentration part 82 and a low concentration part 84.

In the second semiconductor layer 80, an impurity concentration of thehigh concentration part 82 is higher than an impurity concentration ofthe low concentration part 84. The high concentration part 82 isdisposed on the c-plane 60 a of the light emitting layer 60 via thesecond optical confinement layer 70 and the electron blocking layer 72.The high concentration part 82 is not disposed on the facet plane 60 bof the light emitting layer 60. In the illustrated example, the highconcentration part 82 is disposed on the c-plane 72 a of the electronblocking layer 72. The high concentration part 82 is not disposed on thefacet plane 72 b of the electron blocking layer 72. A diametrical sizeD4 at the high concentration part 82 side of the light emitting layer 60is larger than a diametrical size D5 at the light emitting layer 60 sideof the high concentration part 82. The diametrical size D4 is adiametrical size in a portion the closest to the high concentration part82 in the light emitting layer 60. In the illustrated example, thediametrical size D4 is a diametrical size in a contact portion of thelight emitting layer 60 with the second optical confinement layer 70.The diametrical size D5 is a diametrical size in a portion the closestto the light emitting layer 60 in the high concentration part 82. In theillustrated example, the diametrical size D5 is a diametrical size in acontact portion of the high concentration part 82 with the electronblocking layer 72.

The high concentration part 82 of the second semiconductor layer 80 hasa first surface 82 a at the light emitting layer 60 side, and a secondsurface 82 b at an opposite side to the light emitting layer 60. In theillustrated example, the first surface 82 a is a contact surface of thehigh concentration part 82 with the electron blocking layer 72. Thesecond surface 82 b is, for example, a contact surface of the highconcentration part 82 with the second electrode 112. The area of thesecond surface 82 b is larger than the area of the first surface 82 a.For example, when the planar shape of the columnar part 30 is a polygon,a diametrical size D6 of the minimum bounding circle of the secondsurface 82 b is larger than the diametrical size D5 of the minimumbounding circle of the first surface 82 a in the plan view.

In the second semiconductor layer 80, the impurity concentration of thelow concentration part 84 is lower than the impurity concentration ofthe high concentration part 82. The low concentration part 84 surroundsthe high concentration part 82 in the plan view. The low concentrationpart 84 is disposed on the facet plane 60 b of the light emitting layer60 via the electron blocking layer 72. The low concentration part 84 isnot disposed on the c-plane 60 a of the light emitting layer 60. In theillustrated example, the low concentration part 84 is disposed on thefacet plane 72 b of the electron blocking layer 72. The lowconcentration part 84 is not disposed on the c-plane 72 a of theelectron blocking layer 72. The fact that the impurity concentration ofthe low concentration part 84 is lower than the impurity concentrationof the high concentration part 82 can be confirmed by, for example, theatom probe analysis method.

The second semiconductor layer 80 has a contact portion 86 havingcontact with the third semiconductor layer 102. In the illustratedexample, the contact portion 86 of the second semiconductor layer 80 hascontact with the electron blocking layer 72 of the third semiconductorlayer 102. Here, FIG. 3 is a plan view schematically showing thecolumnar part 30. As shown in FIG. 3, in the plan view, for example, inthe contact portion 86, an overlapping portion 86 a overlapping an outeredge 6 of the c-plane 60 a of the light emitting layer 60 is lower inimpurity concentration than the center C of the contact portion 86. Forexample, the impurity concentration of an outer edge 86 b of the contactportion 86 is lower than the impurity concentration at the center C ofthe contact portion 86. The c-plane 60 a of the light emitting layer 60is an end part at the second semiconductor layer 80 side of the lightemitting layer 60. In the illustrated example, the c-plane 60 a is theend part at the high concentration part 82 side of the light emittinglayer 60.

In the light emitting device 100, a pin diode is constituted by, forexample, the second semiconductor layer 80 of the p type, the electronblocking layer 72 of the p type, the second optical confinement layer 70of the p type, the light emitting layer 60 of the i type, the holeblocking layer 52 of the n type, the first optical confinement layer 50of the n type, and the first semiconductor layer 40 of the n type. Inthe light emitting device 100, when applying a forward bias voltage ofthe pin diode between the first electrode 110 and the second electrode112, the electrical current is injected into the light emitting layer60, and recombination of electrons and holes occurs in the lightemitting layer 60. The recombination causes light emission. The lightgenerated in the light emitting layer 60 propagates in an in-planedirection to form a standing wave due to the effect of the photoniccrystal caused by the plurality of columnar parts 30, and is then gainedby the light emitting layer 60 to cause laser oscillation. Then, thelight emitting device 100 emits positive first-order diffracted lightand negative first-order diffracted light as a laser beam in thelaminating direction.

As shown in FIG. 1, the light propagation layer 90 is disposed betweenthe columnar parts 30 adjacent to each other. In the plan view, thelight propagation layer 90 is disposed around the columnar part 30. Thelight propagation layer 90 is, for example, a silicon oxide layer, analuminum oxide layer, or a titanium oxide layer. The light generated inthe light emitting layer 60 can pass through the light propagation layer90 to propagate in the in-plain direction. It should be noted that anair gap can be disposed between the columnar parts 30 adjacent to eachother without disposing the light propagation layer 90 although notshown in the drawings.

The first electrode 110 is disposed on the buffer layer 22. It is alsopossible for the buffer layer 22 to have ohmic contact with the firstelectrode 110. The first electrode 110 is electrically coupled to thefirst semiconductor layer 40. In the illustrated example, the firstelectrode 110 is electrically coupled to the first semiconductor layer40 via the buffer layer 22. The first electrode 110 is one of theelectrodes for injecting the electrical current into the light emittinglayer 60. As the first electrode 110, there is used, for example, whatis obtained by stacking a Cr layer, an Ni layer, and an Au layer in thisorder from the buffer layer 22 side.

The second electrode 112 is disposed on the second semiconductor layer80. The second electrode 112 is electrically coupled to the secondsemiconductor layer 80. The second electrode 112 is the other of theelectrodes for injecting the electrical current into the light emittinglayer 60. As the second electrode 112, there is used, for example, ITO(indium tin oxide). It should be noted that although not shown in thedrawings, a contact layer can also be disposed between the secondsemiconductor layer 80 and the second electrode 112. The contact layeris, for example, a p-type GaN layer.

It should be noted that although the light emitting layer 60 of theInGaN type is described above, as the light emitting layer 60, there canbe used a variety of types of material system capable of emitting lightin response to injection of an electrical current in accordance with thewavelength of the light to be emitted. It is possible to usesemiconductor materials of, for example, an AlGaN type, an AlGaAs type,an InGaAs type, an InGaAsP type, an InP type, a GaP type, or an AlGaPtype.

The light emitting device 100 can exert, for example, the followingfunctions and advantages.

In the light emitting device 100, the second semiconductor layer 80 hasthe high concentration part (a first portion) 82, and a lowconcentration part (a second portion) 84 which surrounds the highconcentration part 82 in the plan view, and is lower in impurityconcentration than the high concentration part 82. Therefore, it ispossible to reduce the electrical current on the side surface of thecolumnar part 30 where the crystal fault is apt to occur. Thus, it ispossible to reduce the leakage of the electrical current between thefirst semiconductor layer 40 and the second semiconductor layer 80. As aresult, in the light emitting device 100, it is possible to efficientlyinject the electrical current into the light emitting layer 60.

In the light emitting device 100, in the contact portion 86 havingcontact with the third semiconductor layer 102 in the secondsemiconductor layer 80, the impurity concentration of the overlappingportion 86 a overlapping the outer edge 6 of the c-plane 60 a of thelight emitting layer 60 in the plan view is lower than the impurityconcentration at the center C of the contact portion 86, and theimpurity concentration in the outer edge 86 b of the contact portion 86is lower than the impurity concentration at the center C of the contactportion 86. Therefore, in the light emitting device 100, it is possibleto reduce the electrical current to be injected into the side surfaceformed of the facet plane 60 b of the light emitting layer 60. Thus, itis possible to reduce the leakage of the electrical current between thefirst semiconductor layer 40 and the second semiconductor layer 80. Thecrystal fault is more apt to occur in the facet plane 60 b of the lightemitting layer 60 than in the c-plane 60 a of the light emitting layer60.

In the light emitting device 100, the diametrical size D4 at the highconcentration part 82 side of the light emitting layer 60 is larger thanthe diametrical size D5 at the light emitting layer 60 side of the highconcentration part 82. Therefore, in the light emitting device 100, itis possible to prevent the high concentration part 82 which is low inresistance and through which the electrical current is apt to flow andthe side surface formed of the facet plane 60 b of the light emittinglayer 60 from having contact with each other. Thus, in the lightemitting device 100, it is possible to reduce the electrical current tobe injected into the facet plane 60 b of the light emitting layer 60compared to when, for example, the diametrical size D4 at the highconcentration part 82 side of the light emitting layer 60 is no largerthan the diametrical size D5 at the light emitting layer 60 side of thehigh concentration part 82 as shown in FIG. 4. Thus, it is possible toreduce the leakage of the electrical current between the firstsemiconductor layer 40 and the second semiconductor layer 80. It shouldbe noted that FIG. 4 is a cross-sectional view schematically showing oneof the columnar parts 30 of a light emitting device 200 according to amodified example of the present embodiment.

In the light emitting device 100, the first semiconductor layer 40 hasthe high concentration part (a third portion) 42, and a lowconcentration part (a fourth portion) 44 which surrounds the highconcentration part 42 in the plan view, and is lower in impurityconcentration than the high concentration part 42. Therefore, in thelight emitting device 100, it is possible to reduce the leakage of theelectrical current between the first semiconductor layer 40 and thesecond semiconductor layer 80 compared to when the impurityconcentration of the fourth portion is the same as the impurityconcentration of the third portion.

In the light emitting device 100, the diametrical size D3 at the highconcentration part 42 side of the light emitting layer 60 is larger thanthe diametrical size D2 at the light emitting layer 60 side of the highconcentration part 42. Therefore, in the light emitting device 100, itis possible to reduce the leakage of the electrical current between thefirst semiconductor layer 40 and the second semiconductor layer 80compared to when the diametrical size D3 is no larger than thediametrical size D2.

In the light emitting device 100, there is provided the second electrode112 disposed on the laminated structure 20, the high concentration part82 has the first surface 82 a at the light emitting layer 60 side, andthe second surface 82 b at the second electrode 112 side, and the areaof the second surface 82 b is larger than the area of the first surface82 a. Therefore, in the light emitting device 100, it is possible tolower the contact resistance between, for example, the columnar parts 30and the second electrode 112 compared to when the area of the secondsurface is no larger than the area of the first surface.

In the light emitting device 100, there is provided the hole blockinglayer 52 disposed between the first semiconductor layer 40 and the lightemitting layer 60, and the first semiconductor layer 40 is the n-typesemiconductor layer, and the second semiconductor layer 80 is the p-typesemiconductor layer. Therefore, in the light emitting device 100, it ispossible to reduce the holes to be leaked from the light emitting layer60 toward the first semiconductor layer 40.

In the light emitting device 100, the light emitting layer 60 has thec-plane 60 a and the facet plane 60 b, the high concentration part 82 isdisposed on the c-plane 60 a, and the low concentration part 84 isdisposed on the facet plane 60 b. Therefore, in the light emittingdevice 100, it is possible to reduce the leakage of the electricalcurrent between the first semiconductor layer 40 and the secondsemiconductor layer 80 compared to when the high concentration part isdisposed on the facet plane.

2. Method of Manufacturing Light Emitting Device

Then, a method of manufacturing the light emitting device 100 accordingto the present embodiment will be described with reference to thedrawings. FIG. 5 is a cross-sectional view schematically showing themanufacturing process of the light emitting device 100 according to thepresent embodiment.

As shown in FIG. 5, the buffer layer 22 is grown epitaxially on thesubstrate 10. As the method of achieving the epitaxial growth, there canbe cited, for example, an MOCVD (Metal Organic Chemical VaporDeposition) method and an MBE (Molecular Beam Epitaxy) method.

Then, a mask layer not shown is formed on the buffer layer 22. The masklayer is formed using, for example, a sputtering method. When growingthe columnar parts 30 using the MOCVD method, the mask layer is, forexample, a silicon oxide layer. When growing the columnar parts 30 usingthe MBE method, the mask layer is, for example, a titanium layer. Then,opening parts are formed in the mask layer. The opening parts are formedby, for example, patterning using the photolithography process and theetching process.

Then, the columnar parts 30 are grown epitaxially on the buffer layer 22using the mask layer as a mask. Specifically, as shown in FIG. 2, thefirst semiconductor layer 40, the first optical confinement layer 50,the hole blocking layer 52, the light emitting layer 60, the secondoptical confinement layer 70, the electron blocking layer 72, and thesecond semiconductor layer 80 are grown epitaxially. As the method ofachieving the epitaxial growth, there can be cited, for example, theMOCVD method and the MBE method.

The growth of the first semiconductor layer 40 is performed whileadjusting, for example, the deposition temperature and the depositionspeed so that the low concentration part 44 surrounds the highconcentration part 42 in the plan view. The impurity concentration ofthe first semiconductor layer 40 is apt to be higher in a centralportion compared to a rim portion. Further, the growth of the firstsemiconductor layer 40 is performed while adjusting, for example, thedeposition temperature and the deposition speed so that the diametricalsize D2 becomes smaller than the diametrical size D1.

The growth of the hole blocking layer 52 is performed while adjusting,for example, the deposition temperature and the deposition speed so thatthe hole blocking layer 52 is provided with the c-plane 52 a and thefacet plane 52 b.

The growth of the light emitting layer 60 is performed while adjusting,for example, the deposition temperature and the deposition speed so thatthe barrier layer 64 surrounds the well layer 62 in the plan view.Further, the growth of the light emitting layer 60 is performed whileadjusting, for example, the deposition temperature and the depositionspeed so that the light emitting layer 60 is provided with the c-plane60 a and the facet plane 60 b, and the diametrical size D4 becomeslarger than the diametrical size D3.

The growth of the second optical confinement layer 70 is performed whileadjusting, for example, the deposition temperature and the depositionspeed so that the second optical confinement layer 70 is provided withthe c-plane 70 a and the facet plane 70 b.

The growth of the electron blocking layer 72 is performed whileadjusting, for example, the deposition temperature and the depositionspeed so that the electron blocking layer 72 is provided with thec-plane 72 a and the facet plane 72 b.

The growth of the second semiconductor layer 80 is performed whileadjusting, for example, the deposition temperature and the depositionspeed so that the low concentration part 84 surrounds the highconcentration part 82 in the plan view. The impurity concentration ofthe second semiconductor layer 80 is apt to be higher in a centralportion compared to a rim portion. Further, the growth of the secondsemiconductor layer 80 is performed while adjusting, for example, thedeposition temperature and the deposition speed so that the diametricalsize D6 becomes larger than the diametrical size D5.

As shown in FIG. 1, the light propagation layer 90 is formed between thecolumnar parts 30 adjacent to each other. The light propagation layer 90is formed using, for example, a spin coat method, ora CVD (ChemicalVapor Deposition) method.

Then, the second electrode 112 is formed on the second semiconductorlayer 80. Then, the first electrode 110 is formed on the buffer layer22. The first electrode 110 and the second electrode 112 are formedusing, for example, a vacuum vapor deposition method. It should be notedthat the order of forming the first electrode 110 and the secondelectrode 112 is not particularly limited.

Due to the process described hereinabove, it is possible to manufacturethe light emitting device 100.

It should be noted that although not shown in the drawings, it ispossible to form a portion having the columnar parts 30 on the substrate10, then remove the substrate 10, and then mount the portion having thecolumnar parts 30 on another substrate. It is possible for the portionhaving the columnar parts 30 to be constituted by the columnar parts 30,the light propagation layer 90, and the second electrode 112, andfurther include the buffer layer 22 and the first electrode 110.

3. Projector

Then, a projector according to the present embodiment will be describedwith reference to the drawings. FIG. 6 is a diagram schematicallyshowing the projector 900 according to the present embodiment.

The projector 900 has, for example, the light emitting device 100 as alight source.

The projector 900 includes a housing not shown, a red light source 100R,a green light source 100G, and a blue light source 100B which aredisposed inside the housing, and respectively emit red light, greenlight, and blue light. It should be noted that in FIG. 6, the red lightsource 100R, the green light source 100G, and the blue light source 100Bare simplified for the sake of convenience.

The projector 900 further includes a first optical element 902R, asecond optical element 902G, a third optical element 902B, a first lightmodulation device 904R, a second light modulation device 904G, a thirdlight modulation device 904B, and a projection device 908 all installedinside the housing. The first light modulation device 904R, the secondlight modulation device 904G, and the third light modulation device 904Bare each, for example, a transmissive liquid crystal light valve. Theprojection device 908 is, for example, a projection lens.

The light emitted from the red light source 100R enters the firstoptical element 902R. The light emitted from the red light source 100Ris collected by the first optical element 902R. It should be noted thatthe first optical element 902R can be provided with other functions thanthe light collection. The same applies to the second optical element902G and the third optical element 902B described later.

The light collected by the first optical element 902R enters the firstlight modulation device 904R. The first light modulation device 904Rmodulates the incident light in accordance with image information. Then,the projection device 908 projects an image formed by the first lightmodulation device 904R on a screen 910 in an enlarged manner.

The light emitted from the green light source 100G enters the secondoptical element 902G. The light emitted from the green light source 100Gis collected by the second optical element 902G.

The light collected by the second optical element 902G enters the secondlight modulation device 904G. The second light modulation device 904Gmodulates the incident light in accordance with the image information.Then, the projection device 908 projects an image formed by the secondlight modulation device 904G on the screen 910 in an enlarged manner.

The light emitted from the blue light source 100B enters the thirdoptical element 902B. The light emitted from the blue light source 100Bis collected by the third optical element 902B.

The light collected by the third optical element 902B enters the thirdlight modulation device 904B. The third light modulation device 904Bmodulates the incident light in accordance with the image information.Then, the projection device 908 projects an image formed by the thirdlight modulation device 904B on the screen 910 in an enlarged manner.

Further, it is possible for the projector 900 to include a crossdichroic prism 906 for combining the light emitted from the first lightmodulation device 904R, the light emitted from the second lightmodulation device 904G, and the light emitted from the third lightmodulation device 904B with each other to guide the light thus combinedto the projection device 908.

The three colors of light respectively modulated by the first lightmodulation device 904R, the second light modulation device 904G, and thethird light modulation device 904B enter the cross dichroic prism 906.The cross dichroic prism 906 is formed by bonding four rectangularprisms to each other, and is provided with a dielectric multilayer filmfor reflecting the red light and a dielectric multilayer film forreflecting the blue light disposed on the inside surfaces. The threecolors of light are combined with each other by these dielectricmultilayer films, and thus, the light representing a color image isformed. Then, the light thus combined is projected on the screen 910 bythe projection device 908, and thus, an enlarged image is displayed.

It should be noted that it is possible for the red light source 100R,the green light source 100G, and the blue light source 100B to directlyform the images by controlling the light emitting devices 100 as thepixels of the image in accordance with the image information withoutusing the first light modulation device 904R, the second lightmodulation device 904G, and the third light modulation device 904B.Then, it is also possible for the projection device 908 to project theimages formed by the red light source 100R, the green light source 100G,and the blue light source 100B on the screen 910 in an enlarged manner.

Further, although the transmissive liquid crystal light valves are usedas the light modulation devices in the example described above, it isalso possible to use light valves other than the liquid crystal lightvalves, or to use reflective light valves. As such light valves, therecan be cited, for example, reflective liquid crystal light valves andDigital Micromirror Device™. Further, the configuration of theprojection device is appropriately modified in accordance with the typeof the light valves used.

Further, it is also possible to apply the light source to a light sourcedevice of a scanning type image display device having a scanning unit asan image forming device for scanning the surface of the screen with thelight from the light source to thereby display an image with a desiredsize on the display surface.

The light emitting devices according to the embodiment described abovecan also be used for other devices than projectors. As the applicationsother than projectors, there can be cited, for example, a light sourceof indoor and outdoor illumination, a backlight for a display, a laserprinter, a scanner, an in-car light, sensing equipment using light,communication equipment, and so on.

The present disclosure includes configurations substantially the same asthe configuration described as the embodiment, for example,configurations having the same function, the same way, and the sameresult, or configurations having the same object and the same advantage.Further, the present disclosure includes configurations obtained byreplacing a non-essential part of the configuration described as theembodiment. Further, the present disclosure includes configurationsproviding the same functions and advantages, and configurations capableof achieving the same object as those of the configuration described asthe embodiment. Further, the present disclosure includes configurationsobtained by adding known technologies to the configuration described asthe embodiment.

The following contents derive from the embodiment and the modifiedexamples described above.

A light emitting device according to an aspect includes a laminatedstructure having a plurality of columnar parts, wherein the columnarpart includes a first semiconductor layer, a second semiconductor layerdifferent in conductivity type from the first semiconductor layer, and athird semiconductor layer disposed between the first semiconductor layerand the second semiconductor layer, the third semiconductor layer has alight emitting layer, and the second semiconductor layer includes afirst portion, and a second portion which surrounds the first portion ina plan view from a laminating direction of the first semiconductor layerand the light emitting layer, and is lower in impurity concentrationthan the first portion.

According to this light emitting device, it is possible to reduce theelectrical current on the side surface of the columnar part where thecrystal fault is apt to occur. Thus, it is possible to reduce theleakage of the electrical current between the first semiconductor layerand the second semiconductor layer. As a result, it is possible toefficiently inject the current into the light emitting layer.

In the light emitting device according to the aspect, in a contactportion having contact with the third semiconductor layer in the secondsemiconductor layer, an impurity concentration in a portion overlappingan outer edge of an end part at the second semiconductor layer side ofthe light emitting layer in the plan view from the laminating directionmay be lower than an impurity concentration at a center of the contactportion, and an impurity concentration in an outer edge of the contactportion may be lower than the impurity concentration at the center ofthe contact portion.

According to this light emitting device, it is possible to reduce theelectrical current to be injected into the side surface formed of thefacet plane of the light emitting layer. Thus, it is possible to reducethe leakage of the electrical current between the first semiconductorlayer and the second semiconductor layer. The crystal fault is more aptto occur in the facet plane of the light emitting layer than in thec-plane of the light emitting layer.

In the light emitting device according to the aspect, a diametrical sizeat the first portion side of the light emitting layer may be larger thana diametrical size at the light emitting layer side of the firstportion.

According to this light emitting device, it is possible to prevent thefirst portion which is low in resistance and through which theelectrical current is apt to flow, and the side surface of the lightemitting layer from having contact with each other. Therefore, it ispossible to reduce the electrical current injected into the side surfaceof the light emitting layer. Thus, it is possible to reduce the leakageof the electrical current between the first semiconductor layer and thesecond semiconductor layer.

In the light emitting device according to the aspect, the firstsemiconductor layer may include a third portion, and a fourth portionwhich surrounds the third portion in the plan view from the laminatingdirection of the first semiconductor layer and the light emitting layer,and is lower in impurity concentration than the third portion.

According to the light emitting device, it is possible to reduce theleakage of the electrical current between the first semiconductor layerand the second semiconductor layer compared to when the impurityconcentration of the fourth portion is the same as the impurityconcentration of the third portion.

In the light emitting device according to the aspect, a diametrical sizeat the light emitting layer side of the third portion may be larger thana diametrical size at an opposite side to the light emitting layer ofthe third portion.

According to this light emitting device, it is possible to increase adifference between an average refractive index in the in-plane directionin the first semiconductor layer and an average refractive index in thein-plane direction in an active layer compared to when the diametricalsize of the third portion is constant (constant at the diametrical sizeat the opposite side to the light emitting layer in the laminatingdirection). Thus, it is possible to further confine the light in theactive layer.

In the light emitting device according to the aspect, a diametrical sizeat the third portion side of the light emitting layer may be larger thana diametrical size at the light emitting layer side of the thirdportion.

According to this light emitting device, it is possible to reduce theleakage of the electrical current between the first semiconductor layerand the second semiconductor layer compared to when the diametrical sizeat the third portion side of the light emitting layer is no larger thanthe diametrical size at the light emitting layer side of the thirdportion.

In the light emitting device according to the aspect, there may furtherbe included an electrode provided to the laminated structure, whereinthe second semiconductor layer may be disposed between the lightemitting layer and the electrode.

In the light emitting device according to the aspect, the first portionmay include a first surface at the light emitting layer side and asecond surface at the electrode side, and an area of the second surfacemay be larger than an area of the first surface.

According to this light emitting device, it is possible to lower thecontact resistance between, for example, the columnar parts and thesecond electrode compared to when the area of the second surface is nolarger than the area of the first surface.

In the light emitting device according to the aspect, there may furtherbe included a hole blocking layer disposed between the firstsemiconductor layer and the light emitting layer, wherein the firstsemiconductor layer may be an n-type semiconductor layer, and the secondsemiconductor layer may be a p-type semiconductor layer.

According to this light emitting device, it is possible to reduce theholes leaking from the light emitting layer toward the firstsemiconductor layer.

In the light emitting device according to the aspect, the light emittinglayer may have a c-plane and a facet plane, the first portion may bedisposed on the c-plane, and the second portion may be disposed on thefacet plane.

According to this light emitting device, it is possible to reduce theleakage of the electrical current between the first semiconductor layerand the second semiconductor layer compared to when the first portion isdisposed on the facet plane.

A projector according to another aspect includes the light emittingdevice according to the above aspect.

What is claimed is:
 1. A light emitting device comprising: a laminatedstructure having a plurality of columnar parts, wherein the columnarpart includes a first semiconductor layer, a second semiconductor layerdifferent in conductivity type from the first semiconductor layer, and athird semiconductor layer disposed between the first semiconductor layerand the second semiconductor layer, the third semiconductor layerincludes a light emitting layer, and the second semiconductor layerincludes a first portion, and a second portion which surrounds the firstportion in a plan view from a laminating direction of the firstsemiconductor layer and the light emitting layer, and is lower inimpurity concentration than the first portion.
 2. The light emittingdevice according to claim 1, wherein in a contact portion having contactwith the third semiconductor layer in the second semiconductor layer, animpurity concentration in a portion overlapping an outer edge of an endpart at the second semiconductor layer side of the light emitting layerin the plan view from the laminating direction is lower than an impurityconcentration at a center of the contact portion, and an impurityconcentration in an outer edge of the contact portion is lower than theimpurity concentration at the center of the contact portion.
 3. Thelight emitting device according to claim 1, wherein a diametrical sizeat the first portion side of the light emitting layer is larger than adiametrical size at the light emitting layer side of the first portion.4. The light emitting device according to claim 3, wherein the firstsemiconductor layer includes a third portion, and a fourth portion whichsurrounds the third portion in the plan view from the laminatingdirection, and is lower in impurity concentration than the thirdportion.
 5. The light emitting device according to claim 4, wherein adiametrical size at the light emitting layer side of the third portionis smaller than a diametrical size at an opposite side to the lightemitting layer of the third portion.
 6. The light emitting deviceaccording to claim 4, wherein a diametrical size at the third portionside of the light emitting layer is larger than a diametrical size atthe light emitting layer side of the third portion.
 7. The lightemitting device according to claim 1, further comprising: an electrodeprovided to the laminated structure, wherein the second semiconductorlayer is disposed between the light emitting layer and the electrode. 8.The light emitting device according to claim 7, wherein the firstportion includes a first surface at the light emitting layer side and asecond surface at the electrode side, and an area of the second surfaceis larger than an area of the first surface.
 9. The light emittingdevice according to claim 1, further comprising: a hole blocking layerdisposed between the first semiconductor layer and the light emittinglayer, wherein the first semiconductor layer is an n-type semiconductorlayer, and the second semiconductor layer is a p-type semiconductorlayer.
 10. The light emitting device according to claim 1, wherein thelight emitting layer has a c-plane and a facet plane, the first portionis disposed on the c-plane, and the second portion is disposed on thefacet plane.
 11. A projector comprising: the light emitting deviceaccording to claim 1.